The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
This invention relates to methods for servicing subterranean wells, in particular, fluid compositions and methods for remedial operations during which the fluid compositions are pumped into a wellbore and make contact with well cements placed during primary cementing or previous remedial cementing operations.
During construction of a subterranean well, remedial operations may be required to maintain wellbore integrity during drilling, to cure drilling problems, or to repair defective primary cement jobs. Wellbore integrity may be compromised when drilling through mechanically weak formations, leading to hole enlargement. Cement slurries may be used to seal and consolidate the borehole walls. Remedial cementing is a common way to repair defective primary cement jobs, to either allow further drilling or to provide adequate zonal isolation for efficient well production.
During well production, remedial cementing operations may be performed to restore production, change production characteristics (e.g., to alter the gas/oil ratio or control water production), or repair corroded tubulars.
During a stimulation treatment, the treatment fluids must enter the target zones and not leak behind the casing. If poor zonal isolation behind the production casing is suspected, a remedial cementing treatment may be necessary.
Well abandonment frequently involves placing cement plugs to ensure long-term zonal isolation between geological formations, replicating the previous natural barriers between zones. However, before a well can be abandoned, annular leaks must be sealed. Squeeze cementing techniques may be applied for this purpose.
Common cementitious-fluid systems employed during squeeze-cementing operations include, Portland cement slurries, calcium-aluminate cement slurries, and organic resins based on epoxies or furans.
Portland cement slurries prepared from, for example, ISO/API Class H or Class G cement, are by far the most common cementitious fluids employed in remedial cementing operations. They perform satisfactorily in many applications; however, when the size of the void from which fluid leakage occurs is very small, the cement-particle size may be too large to enter and seal the void. This problem has been mitigated to a significant extent by grinding Portland cement clinker to a finer particle-size distribution. An example of a fine-particle-size, or “microfine,” Portland cement system is SqueezeCRETE™, available from Schlumberger. Generally, SqueezeCRETE systems are capable of sealing voids or cracks as small as about 100 micrometers.
Despite the success of microfine cements, leaks may still occur when the voids or cracks in the cement sheath are smaller than 100 micrometers. It is therefore desirable to provide means to seal such small voids and cracks in or adjacent to the cement sheath and provide zonal isolation.